[1] Bilkent Univ, UNAM, Natl Nanotechnol Res Ctr, TR-06800 Ankara, Turkey
[2] Bilkent Univ, Inst Mat Sci & Nanotechnol, TR-06800 Ankara, Turkey
[3] Bilkent Univ, Dept Phys, TR-06800 Ankara, Turkey
[4] Cairo Univ, Egypt Nanotechnol Ctr, Giza 12588, Egypt